A REMARKABLY LUMINOUS GALAXY AT Z=11.1 MEASURED WITH HUBBLE SPACE TELESCOPE GRISM SPECTROSCOPY

We present Hubble WFC3/IR slitless grism spectra of a remarkably bright z greater than or similar to 10 galaxy candidate, GN-z11, identified initially from CANDELS/GOODS-N imaging data. A significant spectroscopic continuum break is detected at lambda = 1.47 +/- 0.01 mu m. The new grism data, combined with the photometric data, rule out all plausible lower redshift solutions for this source. The only viable solution is that this continuum break is the Lya break redshifted to z(grism) = 11.09(-0.12)(+0.08), just similar to 400Myr after the Big Bang. This observation extends the current spectroscopic frontier by 150 Myr to well before the Planck (instantaneous) cosmic reionization peak at z similar to 8.8, demonstrating that galaxy build-up was well underway early in the reionization epoch at z. >. 10. GN-z11 is remarkably, and unexpectedly, luminous for a galaxy at such an early time: its UV luminosity is 3x. larger than L-* measured at z similar to 6-8. The Spitzer IRAC detections up to 4.5 mu m of this galaxy are consistent with a stellar mass of similar to 10(9) M-circle dot. This spectroscopic redshift measurement suggests that James Webb Space Telescope (JWST) will be able to similarly and easily confirm such sources at z > 10 and characterize their physical properties through detailed spectroscopy. Furthermore, WFIRST, with its wide-field near-IR imaging, would find large numbers of similar galaxies and contribute greatly to JWST ' s spectroscopy, if it is launched early enough to overlap with JWST.